这是什么意思：“document.write（'<scr'+'ipt ...”？

Question

I've seen this on every Yahoo! news page , at the bottom of the source code,
and failed to understand why they break the script word like that.

Does anybody know if there's any reason for this?

document.write("<scr"+"ipt language=javascript src=http://l.yimg.com/d/lib/bc/bc_2.0.4.js></scr"+"ipt>");

Answer 1

Consider this simplified example:

<script>
document.write("something </script> something");
</script>

The browser's HTML parser would see the </script> within the JavaScript string and interpret that as the end of the script element.

The HTML parser doesn't know about JavaScript syntax - all it knows is that the <script> element ends at the next </script> .

(It also knows that you can't have nested <script> elements, hence the breaking of the opening <script> as well as the closing </script> in your example.)

Answer 2

Suppose you are writing a tool that detects the beginning and end of script blocks in a chunk of text. Suppose you see

<blah><blahdeblah><script>

blah blah blah

blah

print("</script>")

print("<script>")

blah

</script>

</blahdeblah></blah>

Without knowing the syntax of the script language, how does your tool know that this is ONE script block and not TWO script blocks with ")blah between them?

A web browser is such a tool. It's a reasonable practice to make sure you never confuse the web browser by never having <script> or </script> in your file unless it actually is a script tag.

Answer 3

这样它就不会被评估，而是作为字符串插入。

Answer 4

这是阻止XML / XHTML和HTML验证器对源代码大吼大叫的一种坏方法。

Answer 5

Some browsers tend to "act" to fast when parsing a document and immediately try to execute the javascript when they find a script tag (even though it is itself in a piece of js). To avoid this they break the decalration of the tag.

Answer 6

For a full discussion of this, see:
http://www.wwco.com/~wls/blog/2007/04/25/using-script-in-a-javascript-literal/

The short answer is that your code is parsed in two discrete steps.

The first one is XML. And that means that the element <SCRIPT> is looking for a </SCRIPT>. It's important to remember that XML elements are content agnostic. That means that the parser doesn't know yet that there's JavaScript in there.

Once it has the contents of the <SCRIPT> element, then it processes that chunk of text, which presumably is JavaScript.

By splitting up the tag with a string concatenate operator you prevent a constant from tripping up the XML phase.

One simple solution is to put &lt; and &gt; in the Javascript text.